Symlinks to files inside sysconfdir are now only installed if
ìnstall_sysconfdir=true (which is the default).
If sshconfdir,sshdconfdir,shellprofiledir are not inside sysconfdir and
install_sysconfidr=false, these symlinks are still installed to the
configured directory.
Now our baseline of meson is 0.62, hence install_symlink() can be used.
Note, install_symlink() implies install_emptydir() for specified
install_dir. Hence, this also drops several unnecessary
install_emptydir() calls.
Note, the function currently does not support 'relative' and 'force' flags,
so several 'ln -frsT' inline calls cannot be replaced.